The present invention relates to perimetric examinations of visual fields. More particularly, the invention relates to a method of displaying the results of perimetric examinations. Still more particularly, the invention relates to a method of graphically displaying data which are obtained from repetitive perimetric examination of the visual field of one and the same subject.
Recent developments in perimetry, especially the computerization of perimeters, render it possible to complete perimetric examination of visual fields within a short interval of time and with a high degree of accuracy. A modern perimeter, e.g., a perimeter known as "OCTOPUS" (trademark) distributed by HITRON Corporation, Norwood, N.J. and INTERZEAG AG, Schlieren, Switzerland, is equipped with a cupola providing an illuminated screen for presentation of stimuli to a subject who is seated in front of the cupola, a computer which selects the sequence and intensity of stimuli as well as the examination program and receives and processes subject responses, an external memory for storage of the results of examinations, a typewriter keyboard connected with the computer, a printer which furnishes a graphical display of a perimetric examination, and certain optional equipment such as a rotary monitor for automatic determination of the direction of gaze. Each program involves the presentation of a group of variable-intensity stimuli at selected points of a lattice-like raster which overlies the visual field. The stimuli (short-lasting spots of light) of each group are presented at random and the intensity of each stimulus is varied until the subject response indicates the presentation of a threshold value, namely, a value which is discernible by the subject's eye with a 50-percent probability. An automatic perimeter stores a substantial number of examination programs including a program for general survey of the entire visual field and programs for the examination of selected areas or portions of such field. The printer furnishes a graphic display of the examination results, i.e., it normally imprints a sheet wherein the threshold values of a selected group of stimuli are represented by numerals, lines of different length or dots of different diameters. A presently preferred method is display by proportional areas (grey tones). The relationship of symbols or individual data on the sheet corresponds to the pattern of stimuli which were presented to the subject in the course of a perimetric examination. The display shows the distribution of threshold values over the entire visual field or over the selected area of the field. Furthermore, the display can show the distribution of threshold values over the selected area of the visual field or in a section along a straight line.
A drawback common to all presently known methods is that it is difficult to piece together the results of several successive examinations, i.e., the ophthalmologist does not obtain a graphic display which constitutes a composite representation of data obtained as a result of two or more discrete examinations of one and the same area or of different areas of the visual field of a subject. In other words, the printer merely furnishes data denoting the results of discrete examinations. The problem is especially pronounced when some or all of successive examinations do not involve the determination of threshold values in different areas of the visual field.